This walled cylindrical workpieces, such as internal combustion engine cylinder liners, are frequently distorted in heat treat to a slightly out-of-round condition.
Removal of finishing stock for the internal diameter involves holding the workpiece in a chuck, or for the external diameter, holding the workpiece on an arbor. Expansion arbors and contracting chucks are well known in the art as applied to relatively rigid workpieces which are not deflected significantly by the holding pressure. However, as applied to thin walled relatively flexible workpieces, a conventional chuck or arbor may deflect the workpiece from its out-of-round condition to a true round cylindrical configuration during the finishing operation. This will establish a true round cylindrical finish surface to final external or external diameter while held by the chuck or arbor but subject to spring back to an out-of-round condition upon removal from the process tooling.
Such remaining out of round condition of the final workpiece may result either where the finishing operation is limited to only one of the external or internal surfaces or where both surfaces are successively finished by final turning, boring or grinding operations.
If the workpiece is to be ultimately mounted with accurate fit within a rigid member, such as an engine block in the case of a cylinder liner, the out-of-round condition may be remedied upon installation by conformity to the rigid member. However, even in the case of cylinder liners, preferred practice involves finishing operations which correct the out-of-round condition for the workpiece in its free state. This involves the requirement for holding the workpiece in a chuck or on an arbor without deflection from its out-of-round condition while finishing stock is removed from one of the external or internal surfaces. If the second surface is then also finished, it may then be held with conventional cylindrical tooling with resulting free state true cylindrical configuration.
One basic approach to providing an arbor or chuck which will hold a thin walled workpiece without deflection from its slightly out-of-round condition is disclosed in U.S. Pat. No. 3,677,559 as a hydrostatic holding device which employs a relatively plastic sleeve, in either internal or external holding units, or pliant material such as nylon which is relatively soft compared to metal parts which are to be clamped, the concept being a sleeve material which will conform to the surface conditions of the part being held and exert pressure thereon without changing the shape of the part. Such patent discloses in the drawings and specification an external chuck type holding unit employing a flexible nylon sleeve of either uniform thickness or of a varying thickness adapted to conform to varying external diameters of the workpiece.